Carbon nanotubes offer attractive possibilities for developing new sensors because of superior mechanical and electrical properties. So far most studies relate to the mechanical deformation and to the change of nano-scale electrical properties. We present an attempt to utilize multi wall carbon nanotubes for developing a new flexible composite for macro-scale pressure sensors. Two simultaneously existing effects—mechanical strain sensing and organic solvent vapour sensing – were found and investigated in polyisoprene-multi wall carbon nanotube composites. Elastomer composites containing dispersed nano-size particles, for example, polyisoprene-multi wall carbon nanotube composites were prepared by treatment of the composite matrix with chloroform providing an increase of mobility and better dispersion of the nano-particles within the matrix. Multi wall carbon nanotubes with a small amount of solvent were carefully grinded in a china pestle before adding the polyisoprene matrix. Both the polyisoprene matrix solution and concentrated multi wall carbon nanotube solution in chloroform were blended at room temperature for certain time in a mixer which contained small glass spheres. The product was dried and vulcanized under 3×106 Pa pressure at 160 C for 20 min. Polyisoprene–multi wall carbon nanotube composites show attractive pressure sensing and gas sensing properties. The maximum sensitivity has been achieved in the region slightly above percolation threshold of the composite. The mechanism of sensing effect is based on changes in tunneling currents due to the strain caused by mechanical forces as well as swelling of composite matrix.